Quantitative Analysis of Metabolites

Optima^™ LC/MS grade formic acid and high performance liquid chromatography (HPLC) grade water were purchased from Fisher Scientific (Ottawa, CA). Pure reference standard compounds, except 3-(3-hydroxyphenyl)-3-hydroxypropionic acid (HPHPA), were purchased from Sigma-Aldrich (Oakville, CA). ²H-, ¹³C- and ¹⁵N-labelled compounds (except ¹³C-labelled HPHPA), which were used as internal quantification standards for amino acids, biogenic amines, carnitines and derivatives, phosphatidylcholines and their derivatives, were purchased from Cambridge Isotope Laboratories, Inc. (Tewksbury, USA). HPHPA and ¹³C-labelled HPHPA were synthesized in-house as described previously [28 (link)]. Optima^™ LC/MS grade ammonium acetate, phenylisothiocyanate (PITC), 3-nitrophenylhydrazine (3-NPH), 1-ethyl-3-(3-dimethylaminopropyl) carbodiimide (EDC) and butylated hydroxytoluene (BHT), HPLC grade pyridine, HPLC grade methanol, HPLC grade ethanol and HPLC grade acetonitrile (ACN) were purchased from Sigma-Aldrich (Oakville, CA). Nunc^® 96 DeepWell^™ plates were purchased from Sigma-Aldrich (Oakville, CA).